One of the limiting features of downhole thin walled tubulars is collapse strength. Increasing the collapse strengths allows borehole operations to take place that would otherwise not be possible. In other applications where heat transfer is important the surface area of such tubulars is limited. For example in geothermal applications where fluid circulating inside the tubular is heated by the surrounding formation or in the opposite direction where steam is used to get formation hydrocarbons to flow for collection known as steam assisted gravity drain (SAGD) systems, there is a need for enhanced heat transfer surface. More traditional ways to enhance heat transfer surface area used in heat exchangers is to surround the tubular with parallel fins. These fins take up space that is frequently not available in downhole applications. The fins are also thin structures that can easily be damaged in the trip into a borehole, assuming there even was space available to insert such structures.
In the past multiple nested tubulars have been expanded into each other to create a network of gaps for fluid flow in a heat transfer application as shown in US 2011/0114336 where such structures are shown for example in FIG. 2B. Other techniques use flat thin sheet and push a patterned roller onto the sheet against a rubber roller backup to impose the pattern onto the sheet as is shown in U.S. Pat. No. 6,221,299 or WO/1997039846. Creating layered tubulars with one having an imposed pattern attached to another covering tubular are shown in U.S. Pat. No. 5,887,470. These techniques are designed for shop fab facilities and do not translate to applications where the tubular may already be in a borehole. Additionally even in a surface fabrication environment, these structures are multi-walled making them expensive to fabricate and requiring significant outlays for capital equipment.
What is needed is a more versatile method to economically pattern harden a tubular wall or a sheet later formed into a tubular shape and then by differential pressure application after the pattern hardening increase the available heat transfer area while enhancing the collapse resistance of the tubular. The hardening can be accomplished with lasers, electron beam or irradiation treatment coupled with a differential pressure across the wall or using an insert into the tubular and wall differential pressure to emboss a pattern on the tubular wall followed by removal of the insert in a variety of ways. The addition of the profile whether built up or a recess is referred to herein as profiling or contouring. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.